The concept of Wavelength division multiplexing (WDM) is analogous to the basic concept of frequency division multiplexing (FDM) in which the available bandwidth of a communications channel in its frequency domain is divided into multiple sub-bands (called user channels). This technique enables bidirectional communications over a. In the relentless pursuit of higher bandwidth and more efficient fiber utilization, wavelength division multiplexing (WDM) technologies are fundamental. But navigating the alphabet soup of CWDM, DWDM, MWDM, LWDM, and SWDM can be daunting. This allows multiple channels of data to be transmitted simultaneously.